The phrase "decline in marital satisfaction" means that the happiness and contentment felt within a marriage is gradually decreasing over time. Full definition
Marriage research shows that 67 percent of couples report a significant decline in marital satisfaction after the birth of a baby. (psychcentral.com)
But spouses who were more forgiving towards partners, who frequently behaved negatively, experienced sharper declines in marital satisfaction. (positivepsychologynews.com)
A variety of studies have found that about half of couples with a new baby experienced a moderate to severe decline in marital satisfaction. (dadsadventure.com)